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Portland cement concrete (PCC) is the construction material most used worldwide. Hence, its proper characterization is fundamental for the daily-basis engineering practice. Nonetheless, the experimental measurements of the PCC's engineering properties (i.e., Poisson's Ratio -v-, Elastic Modulus -E-, Compressive Strength -ComS-, and Tensile Strength -TenS-) consume considerable amounts of time and financial resources. Therefore, the development of high-precision indirect methods is fundamental. Accordingly, this research proposes a computational model based on deep neural networks (DNNs) to simultaneously predict the v, E, ComS, and TenS. For this purpose, the Long-Term Pavement Performance database was employed as the data source. In this regard, the mix design parameters of the PCC are adopted as input variables. The performance of the DNN model was evaluated with 1:1 lines, goodness-of-fit parameters, Shapley additive explanations assessments, and running time analysis. The results demonstrated that the proposed DNN model exhibited an exactitude higher than 99.8%, with forecasting errors close to zero (0). Consequently, the machine learning-based computational model designed in this investigation is a helpful tool for estimating the PCC's engineering properties when laboratory tests are not attainable. Thus, the main novelty of this study is creating a robust model to determine the v, E, ComS, and TenS by solely considering the mix design parameters. Likewise, the central contribution to the state-of-the-art achieved by the present research effort is the public launch of the developed computational tool through an open-access GitHub repository, which can be utilized by engineers, designers, agencies, and other stakeholders. [ABSTRACT FROM AUTHOR]

Concrete structures undergo integral fragmentation under explosion loads. The fragmentation degree and particle-size distribution of concrete blocks under explosion loads must be considered during mining to ensure safety. In this study, the impulse is calculated based on the relationship between overpressure and time, and the impact energy of the explosion wave is obtained based on blast theory. Subsequently, the Mohr-Coulomb shear strength fracture criterion is introduced to determine the ultimate shear stress of the concrete materials, and an empirical model that can effectively calculate the energy consumption of concrete blocks under explosion loads is established. Furthermore, concrete fragments with different particle sizes under explosion scenarios are quantitatively predicted with the principle of energy conservation. Finally, explosion tests with different top standoff distances are conducted, and the concrete fragments after the explosion tests are recovered, sieved, weighed, and counted to obtain experimental data. The effectiveness of the fragment empirical model is verified by comparing the model calculation results with the experimental data. The proposed model can be used as a reference for civil blasting, protective engineering design, and explosion-damage assessment. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are metallic materials that are characterized by their ability to restore their original shape after large deformation when activated by heating. This unique property renders SMAs appealing for various civil engineering applications. Iron-based SMAs (Fe-SMAs), including alloys like Fe–Mn–Si, stand out due to their cost-effectiveness and high strength. The primary focus of this research lies in the computational modeling of Fe-SMA strips utilized to reinforce damaged concrete structures. To achieve this, details from an experimental test are leveraged for the computational simulation of real-scale reinforced concrete beams that were first loaded to some level of damage, then released and strengthened, and subsequently retested. The strengthening approach involves the application of external Fe-SMA strips wrapping around the beams. This paper presents an original computational modeling setup that incorporates a switch option for the Fe-SMA material. This feature enables one to use a single simulation platform for the whole process. The significance of this method originates from its capacity to ensure a robust analysis that includes all simulation steps-testing unstrengthened beams, installing and heating Fe-SMA strips, and testing both damaged and strengthened beams—in a single, multi-step analysis. The computational simulation results were compared with the outcomes of the experimental test, revealing an acceptable level of agreement. The findings indicate a substantial increase in both shear strength and ductility as a result of the application of Fe-SMA strips. Additionally, parametric and mesh sensitivity studies were conducted. These aimed to investigate the mesh dependency of the model and to identify the optimal mesh size. Furthermore, variations in the details of the Fe-SMA strips, including thickness, width, quantity, and effect of applied temperature were explored to compare the outcomes of different applications of these strips. [ABSTRACT FROM AUTHOR]

The article discusses one of the dangerous geological processes that can cause serious damage to hydraulic engineering construction objects. Using the example of Zagorsk Pumped Storage Power Station-2 (ZaPSPS-2), it is shown how the initial development of suffosion when filling the downstream pool of the hydraulic structure led to the formation of a weakened zone, subsequent destruction, and removal of suffosion-unstable rocks in the contact zone with the reinforced concrete structure. [ABSTRACT FROM AUTHOR]

In this study, comprehensive analytical and parametric studies were conducted on seismic performance of concrete structures equipped with self-centered unbonded post-tensioned hybrid wall system in comparison with traditional structural wall system. For this purpose, analytical models were developed and to further study the seismic performance of self centering hybrid wall, parametric analysis was performed considering four parameters: wall aspect ratio, initial stress of post-tensioned (PT) tendons, the total area of PT tendons, the total area of mild bars. The performance of buildings was evaluated under non-linear quasi cyclic and time history method considering two seismic hazard levels, the design-based earthquake (DBE) level and the risk-targeted maximum considered earthquake (MCE) level. Hysteresis response, damage severity and pattern index estimation, energy dissipation ability and damping ratio, relative self-centering efficiency (RSE), residual drift, peak roof drift and inter-story drift ratio, floors acceleration, shear force ratio, column curvature ductility, prestressing and gap opening effect of all buildings were studied. The results of the parametric analysis showed by increasing the prestressing ratio, wall damage severity, residual drift and energy dissipation capacity were decreased and structural seismic demand and RSE increased, while increasing mild bars was the most efficient method for improving the energy dissipation ability. [ABSTRACT FROM AUTHOR]

This study presents an innovative numerical model based on the position-based finite element method, utilizing laminated frame elements to predict beam displacements under corrosion-a common challenge in reinforced concrete structures due to chlorides and carbon dioxide penetration. The proposed model addresses both geometric and physical non-linearity, specifically considering the uniform reduction in rebar area, a critical consequence of carbonation-induced corrosion. This reduction significantly influences element inertia and, consequently, the structure's stiffness. Given the expected increase in corrosion problems in reinforced concrete structures due to climate change-induced rising temperatures and heightened carbon dioxide levels, resulting in earlier degradation and reduced stiffness, there is a pressing need for alternative approaches to calculate structure displacement under carbonation-induced corrosion. In response to this concern, our model provides an innovative and alternative methodology, demonstrating promising results when compared with existing literature, even under the constraints of a simplified model. [ABSTRACT FROM AUTHOR]

The post-fire assessment of concrete structures is a complex task that requires the integration of multiple measurements from different techniques. The current approach to integrate information from different sources relies mainly on expert judgement, meaning that no explicit consideration is given to the precision of different techniques. This paper presents a Bayesian updating methodology that integrates information from different sources about the maximum temperature the concrete experienced during fire exposure at a certain depth, such as discoloration and rebound hammer measurements, by considering the uncertainties and errors associated with measurements. The data is then used to update the prior information on the uncertain parameters of interest, here the fire load density and opening factor. These updated distributions provide a better estimate of the fire exposure, thermal and damage gradient and the residual condition of the structure. The proof-of-concept and effectiveness of the proposed methodology are demonstrated through a case study. The results show that the proposed methodology is able to effectively incorporate the uncertainties and errors associated with the assessment techniques, producing more reliable estimates of the fire severity. This method has the potential to improve the post-fire assessment process and provide more accurate information for the rehabilitation of concrete structures. [ABSTRACT FROM AUTHOR]

The ultrasonic echo technique is widely used in non-destructive testing (NDT) of concrete objects for thickness measurements, geometry determinations and localization of built-in components. To improve ultrasonic imaging of complex concrete structures, we transferred a seismic imaging technique, the Reverse Time Migration (RTM), to NDT in civil engineering. RTM, in contrast to the conventionally used synthetic aperture focusing technique (SAFT) algorithms, considers all wavefield types and thus, can handle complex wave propagations in any direction with no limit on velocity variations and reflector dip. In this paper, we focused on the development, application and evaluation of a two-dimensional elastic RTM algorithm considering horizontally polarized shear (SH) waves only. We applied the elastic SH RTM routine to synthetic ultrasonic echo SH-wave data generated with a concrete model incorporating several steps and circular cavities. As these features can often be found in real-world NDT use cases, their imaging is extremely important. By using elastic SH RTM, we were able to clearly reproduce almost all reflectors inside the concrete model including the vertical step edges and the cross sections of the cavities. We were also capable to show that more features could be mapped compared to SAFT, and that imaging of complex reflectors could be sharpened compared to elastic P-SV (compressional-vertically polarized shear) RTM. Our promising results illustrate that elastic SH RTM has the potential to significantly enhance the reconstruction of challenging concrete structures, representing an important step forward for precise, high-quality ultrasonic NDT in civil engineering. [ABSTRACT FROM AUTHOR]

Concrete structures are subjected to various levels of damage during their life cycle due to exposure to different environmental and loading conditions. Hence, damage severity prediction and localization in concrete elements remain critical tasks to provide optimal maintenance in a timely manner, leading to reduced maintenance costs and avoiding any catastrophic failure that may cause serious loss and danger to the infrastructure owners. The Acoustic Emission (AE) technique is one of the powerful nondestructive testing (NDT) methodologies that can be used to predict the severity of damage and localize it in different systems. This paper proposes a damage identification approach by combining Multivariate Empirical Mode Decomposition (MEMD) and the Gaussian Mixture Model (GMM). Unlike existing methods that rely on a single AE measurement, MEMD is used to extract the key AE components that belong to cracks using AE data collected from multiple sensors. MEMD is an extended version of EMD that can analyze multichannel AE signals collected from different sensors. The statistical features (e.g., mean, root mean square, kurtosis, skewness, and crest factor) of AE components obtained from MEMD are then subsequently estimated. The selected features are used in the GMM model to predict the severity and qualitative location of the damage. The proposed method is validated using a suite of experimental studies and AE data collected from a full-scale concrete dam located in Ontario, Canada. The results show that the proposed approach can accurately predict the severity of damage and identify the potential location of damage and prove that the proposed method can be suitable for robust damage identification in concrete structures. [ABSTRACT FROM AUTHOR]

In the framework of the international benchmark "Vulcain tests on 3 Walls", three full scale ISO fire tests on a reinforced concrete wall, simultaneously subjected to a constant uniaxial compressive load, were conducted in CSTB in Paris, France. The duration of these tests exceeded 120 min. In order to assess the capability of available finite elements (FE) models to represent reinforced concrete structural behaviour under fire exposure, IRSN, within the scope of the Vulcain benchmark, set up a modelling with help of Mazars isotropic continuum damage mechanical model (Mazars Application de la mécanique de l'endommagement au comportement non linéaire et à la rupture du béton de structure. PhD Thesis, Univ. Paris 6, ENS Cachan, France, 1984) ran with the CAST3M software (Verpeaux et al. in Fouet, Ladevèze and Ohayon (eds), Calcul des Structures et Intelligence Artificielle, Pluralis, 1988), while a user-defined procedure was used to calculate the concrete properties taking into account load induced thermal strains (LITS). The effect of LITS according to the model of Anderberg and Thelandersson (Stress and deformation characteristics of concrete at high temperatures: 2 experimental investigation and material behavior model, Bulletin 54, Lund Institute of Technology, Lund, 1976) was considered by an explicit term in the strain decomposition. Also, the numerical simulation of three full scale ISO fire tests of Vulcain was carried out with the help of a FE model that takes into account the values of the concrete thermomechanical parameters identified. The numerical model is composed of two different parts, one for heat transfer analysis and the other one for structural analysis based on a three-dimensional FE model including concrete and reinforcing steel meshes. It is illustrated through this numerical investigation that the proposed model can predict the thermomechanical behaviour of reinforced concrete walls under fire exposure. [ABSTRACT FROM AUTHOR]

The ultrasonic echo technique is frequently used in non-destructive testing (NDT) of concrete structures for thickness measurements, geometry determinations as well as localization of built-in components. To improve ultrasonic imaging of complex structures in concrete, we transferred a geophysical imaging technique, the reverse time migration (RTM), to NDT in civil engineering. In contrast to the conventionally used synthetic aperture focusing technique (SAFT) algorithms, RTM is a wavefield continuation method in time and uses the full wave equation. Thus, RTM can handle complicated wave propagations in any direction without dip limitation. In this paper, we focused on the application and evaluation of a two-dimensional (2D) elastic RTM algorithm considering compressional waves, vertically polarized shear waves, and Rayleigh waves. We tested the elastic RTM routine on synthetic ultrasonic echo data generated with a 2D concrete model consisting of several steps and circular air inclusions. As these complex structures can often be found in real-world NDT use cases, their imaging is especially important. By using elastic RTM, we were able to clearly reproduce vertical reflectors and lower edges of circular air voids inside our numerical concrete model. Such structures cannot be imaged with conventional SAFT algorithms. Furthermore, the used elastic RTM approach also yielded a better reconstruction of a horizontal reflector and upper boundaries of circular air inclusions. Our encouraging results demonstrate that elastic RTM has the potential to significantly improve the imaging of complex concrete structures and, thus, is a step forward for detailed, high-quality ultrasonic NDT in civil engineering. [ABSTRACT FROM AUTHOR]

The potential of non-metallic reinforcement to be an environmentally sustainable alternative to classic steel reinforcement in concrete has become evident in recent years. The high-performance fibres used to produce non-metallic reinforcement elements have a considerably lower weight to transferable tensile forces ratio and are almost non-corrosive under common exposures. These indicators allow for a high environmental performance throughout the extended life cycle of the product. At the same time, substantially more resources and energy per unit weight are required for their production in some cases, e.g. for carbon fibres, compared to conventional reinforcing steel. The presented work addresses this conflict by closing a number of obvious research gaps. Despite an increasing number of publications during the last years, so far there are no comprehensive sets of data available on the environmental impact of various concrete reinforcing materials. With the data compiled in this work, for the first time, an objective comparison of different reinforcement systems (conventional and alternative) is presented that differentiates various environmental impact categories and therefore enables to perform Life Cycle Assessment (LCA). Other often observed shortcomings in sustainability assessments in concrete constructions are that an extension of the service life due to improved durability and the burden a material poses at the end of its life cycle are not considered. Comprehensive reviews of durability considerations help to develop an estimation of the service life. In addition, a state-of-the-art on possible strategies for dismantling, recycling and reuse of alternative non-metallic reinforcement systems shows that the composition of the FRPs, i.e., fibre and matrix materials, not only has a strong influence on the environmental impact in the production phase, but also on the durability as well as on a possible reuse. [ABSTRACT FROM AUTHOR]

Rapid and accurate detection of internal defects in bridges has always been a major concern of the management and maintenance departments. In the present study, an intelligent method for the detection of structural internal defects is proposed based on infrared thermography and deep learning. Through theoretical analysis, numerical simulations and laboratory experiments, the classification, localization and quantification of internal defects of concrete structures were achieved with the infrared thermography and deep learning method. The mean average precision for classification and localization of internal defects is 96.59%, the mIoU for pixel-level segmentation is 95.19%, and the average relative error for damage quantification is 0.70%. The feasibility of the trained model is verified with new images, and the results show that the trained model can capture infrared thermal features of internal defects with different sizes and depths. This method has the advantages of low cost, high accuracy, easy operation, and large area scanning of concrete structures, which can provide a good reference for the detection of internal defects of concrete structures. [ABSTRACT FROM AUTHOR]

Accurate measurement of dynamic stresses in concrete is important for mechanical analysis and theoretical innovation of concrete materials. In dynamic stress measurements of concrete, the matching error between the transducer and the concrete is the controlling error in the total error. To improve the measurement accuracy, in this study, the dynamic stress test method was investigated by considering the matching error. The propagation law of the time- and frequency-domain characteristics of the concrete stress under an explosion load was obtained through simulation, and the measurability of the stress was analyzed. The installation range and the minimum installation spacing of the transducers was analyzed based on the control of the matching error, and a matching error with a practical value was obtained. A stress transducer installation method was designed to meet the measurement requirements, and explosion tests were carried out. The results show that the peak value and bandwidth of the stress signal decayed rapidly with increasing propagation distance. The peak value decays exponentially, while the bandwidth decreases rapidly in the near field of the explosion to near a stable value and then rises gradually in the region close to the free boundary as the propagation distance increases. The minimum distance of the transducer from the explosives is 25 cm. The minimum distance of the transducer from the concrete boundary is 20 cm. The minimum installation distance of the transducers is 18 times the transducer thickness. [ABSTRACT FROM AUTHOR]

Many of the world's concrete dams are approaching the end of their expected service life and many of these dams are cracked due to environmental effects. It is thus desirable to be able to extend the service life of many of these dams. It is therefore important to develop reliable methods of analysis to assess the current status of these dams and to determine the safety of these, partly damaged structures. A slender reinforced concrete arch dam is used as a case study with the aim of predicting the structural response, the cracks found in-situ and of assessing the safety of the dam. This dam has cracked extensively along the downstream face primarily due to seasonal temperature variations. A detailed finite element model has been developed to simulate the history of the dam with the variations in ambient conditions that have occurred over its lifetime. The results show good agreement regarding both the crack pattern and displacement of the dam. A procedure to simulate a progressive dam failure, starting from the current state, is utilized to assess the current level of safety. The results show that the cracking has a limited effect on the safety factor of the dam. [ABSTRACT FROM AUTHOR]

The ultrasonic approach is one of the non-destructive testing methods that most technologically progressed in past few years. This study aims to validate the accuracy and capabilities of this method in the mechanical characterization of concrete elements, by using an ultrasonic tomography equipment based in echo pulse velocity (S-waves). The elastic modulus and compressive strength of concrete are estimated from the echo pulse velocity. Furthermore, the uniformity of concrete elements is evaluated. The concrete compression strength prediction was performed on cubic specimens and the reached accuracy was over 91% using the analytical approach proposed on this study. The correlation coefficient between the pulse echo velocity and the uniaxial compression strength found in this study was over 97%. Thus, the use of the ultrasonic NDT to evaluate the uniformity of concrete elements proved to be efficient. [ABSTRACT FROM AUTHOR]

The advancements of additive manufacturing (AM) technologies are typically coupled with research addressing topology optimization, whose aim is to use optimization methods to achieve effective expressions of free-form design. While many studies emphasize the breakthroughs that topology optimization could bring into structural engineering, there are just a few scientific contributions that address design feasibility, accounting for the technological constraints that characterize the different AM techniques. By formulating a stress-constrained topology optimization problem with a more technologically oriented approach, this study aims to optimize concrete structures while enforcing the cross-section width and path-traceability restrictions that affect the feasibility and performance of geometries obtained through the layered extrusion technique. In particular, this paper proposes a curve-based Biased Random-Key Genetic Algorithm that optimizes stress-constrained structures and generates topologies that can be implemented without post-processing operations. The proposed algorithm, when tested on a diverse set of concrete beam configurations, effectively achieved optimized solutions that used between 81 % and 75 % less material than the full beam configuration. Additionally, each one of the designed topologies adequately met the stress requirements and process-specific constraints. Lastly, two experimental cases also highlighted the printability effectiveness of the proposed approach in conjunction with design of optimized solutions. [ABSTRACT FROM AUTHOR]

Surface cracks on the concrete structures are a key indicator of structural safety and degradation. To ensure the structural health and reliability of the buildings, frequent structure inspection and monitoring for surface cracks is important. Surface inspection conducted by humans is time-consuming and may produce inconsistent results due to the inspectors' varied empirical knowledge. In the field of structural health monitoring, visual inspection of surface cracks on civil structures using deep learning algorithms has gained considerable attention. However, these vision-based techniques require high-quality images as inputs and depend on high computational power for image classification. Thus, in this study, shallow convolutional neural network (CNN)-based architecture for surface concrete crack detection is proposed. LeNet-5, a well-known CNN architecture, is optimized and trained for image classification using 40,000 images in the Middle East Technical University (METU) dataset. To achieve maximum accuracy for crack detection with minimum computation, the hyperparameters of the proposed model were optimized. The proposed model enables the employment of deep learning algorithms using low-power computational devices for a hassle-free monitoring of civil structures. The performance of the proposed model is compared with those of various pretrained deep learning models, such as VGG16, Inception, and ResNet. The proposed shallow CNN architecture was found to achieve a maximum accuracy of 99.8% in the minimum computation. Better hyperparameter optimization in CNN architecture results in higher accuracy even with a shallow layer stack for enhanced computation. The evaluation results confirm the incorporation of the proposed method with autonomous devices, such as unmanned aerial vehicle, for real-time inspection of surface crack with minimum computation. [ABSTRACT FROM AUTHOR]

Ultrasonic imaging is a useful nondestructive testing technology for visualizing internal structural defects in structures. Despite its utility, since synthetic aperture focusing technique (SAFT) algorithm demands using advanced equipment to superimpose the measurements, this paper introduces a novel approach named CMU-SAFT to broaden applicability of SAFT on conventional ultrasonic data obviating the necessity for matrix antenna array-equipped devices and preventing hyperbolic patterns. To validate the feasibility of the proposed algorithm, experimental tests were conducted on a laboratory-produced concrete specimen including delamination defects at varying depths. Since other reflectives causing distortion in the ultrasonic image can interfere with the signal, the study also evaluated the influences of different noise suppression filters along with their combinations (band pass, wavelet transform, Wiener, and Savitzky–Golay). CMU-SAFT images were constructed using eleven filter combinations, and their performances were quantitatively assessed using signal-to-noise ratio, signal-to-noise and distortion ratio, total harmonic distortion, root mean square, mean squared ratio, mean absolute error and cross-correlation. The most effective filters and performance indices aligning with CMU-SAFT images considering defect depth and scanning width were suggested. The findings of the study revealed the leading potential of CMU-SAFT algorithm to overcome the need for specialized equipment by utilizing recommended filters and indicators under specific conditions. [ABSTRACT FROM AUTHOR]

Currently, one of the main priorities for a government is to realize sustainable development. Strategies are required to protect the global environment, enhance employee health and safety, reduce emissions, and use fuels and raw materials responsibly across all sectors of the economy. Blended Portland cements containing supplementary cementitious materials (SCMs), usually industrial by-products, are excellent examples of industrial ecology. In particular, they offer a solution for reducing environmental impacts from several industries. In fact, with every ton of cement produced, nearly a ton of CO2 is emitted. The use of SCMs as a cement substitution reduces these CO2 emissions, saves non-renewable material sources, minimizes waste, and enhances the properties of the concrete. High-quality SCMs are becoming increasingly restricted. With the growing demands for cement, new sources of SCMs, often called alternative SCMs (ASCMs), will need to be used. However, this brings another challenge, as ASCMs are often comprised of local materials, with smaller volumes and more variable compositions. Accordingly, efficient and rapid methods are necessary for evaluating their performance and reactivity in concrete materials. Moreover, there is a need to characterize the chemical, physical, and mineralogical properties of the ASCMs. This paper presents the requirements for materials to qualify as SCMs, an example of a rapid screening test for assessing the performance of ASCMs, and an inventory of materials with favorable properties. [ABSTRACT FROM AUTHOR]

An artificial neural network (ANN) model and response surface methodology (RSM) were established to estimate the compressive strength of concrete by using the combination of three non-destructive tests (NDT); rebound number, pulse velocity tests and resistance surface. These techniques are utilized in an attempt to increase the reliability of the non-destructive tests in detecting the strength of concrete. These methods were trained using a set of different mixes and at different ages of concrete specimens. In this case, 180 experimental specimens were conducted and their data are published. Then, different neural network topologies and algorithms besides RSM were examined using the given data. The published models are for two combination including the combination of UPV and RN and the combination UPV, RN and SR. The results show that the accuracy of the published models are increased by aging. In addition, it is showed that RSM don’t need calibration process, while its accuracy is enough. Hence, RSM is a promising method to conduct on NDTs and compressive strength prediction, while ANN needs to perform many times to find the best accuracy. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is considered as a method for elemental analysis of concrete in situ. However, the content of chlorine responsible for corrosion of the iron reinforcement may be lower than the LIBS sensitivity needed to detect corrosion in the initial stage. This is especially true for portable LIBS systems without gating and signal amplification. The use of analytical signals of elements in reinforcement corrosion products (Fe, Mn, Cr) when they emerge on the concrete surface is proposed to detect corrosion. It was found that signals of Fe, Mn, and especially Cr could be reliably registered using LIBZ-200 only on surface areas painted with corrosion products. [ABSTRACT FROM AUTHOR]

Abstract Rare suitable sensors are reported till now for the accurate measurement of inner forces at the concrete structures. In this study, a novel sensor is designed and fabricated for the evaluation of inner stress in the concrete structures under dynamical loads. By embedding this sensor in the critical points of the modern concrete structures (e.g. high-rise buildings, large-span bridges, dams, etc.), the heath monitoring of such structures may be easily done. The proposed sensor is a 5 cm × 5 cm × 5 cm cube made of a novel cement-resin-fiber composite matrix. A number of circular piezoelectric sheets with the same polarization alignment are embedded at the center of the cube with the certain distance from each other. The composite material used in the construction of the proposed sensor is in fact a new matrix composed of Portland cement, resin, water, fine silica and polymeric fibers which guarantees the strength, safety and sensitivity of the sensor at high level of stresses. The performance and reliability of the presented sensor has been proved through experimental tests. By considering different range of input force frequency (ω), it was found that the simple exponential law Δ V = 0.8 exp(−0.037 ω)Δ F exists between the amplitude of output sensor (Δ V) and amplitude of input force (Δ F). Compared to optical sensors and other available types of sensors which usually require special fabrication technology, the proposed sensor is low-price and easy to build and install. High sensitivity and precision in the range of 0.5–50 Hz, good compatibility with concrete, high durability, and the generating of strong output signals are other advantages of the proposed sensor. [ABSTRACT FROM AUTHOR]

Many concrete structures, such as high concrete dams and deep tunnels, running perennially under the high water pressure condition, are prone to hydraulic fracturing failure. In this paper, a calculation method of water pressure within cracks is proposed, which can reflect the coupling relationship between water flow in cracks and structure deformation. Meanwhile, a crack propagation criterion of hydraulic fracture is proposed, which can be used to analyze the mixed-mode crack propagation problems considering the high water pressure within crack. Based on the theories of seepage and fracture mechanics, a new coupling analysis model for simulating the hydraulic fracturing in concrete structures is presented by using the element-free method (EFM), and the coupling analysis program (CSWF. for) is developed. Then, this analysis model is verified against two numerical examples, and the numerical results have good agreement with the corresponding the law of tests. Finally, the proposed model is applied to simulate hydraulic fracturing in a high concrete gravity dam. Results show that the crack is developed toward the bottom and the downstream of the dam. The ultimate bearing capacity of the dam would decrease obviously if the water pressure within cracks is considered. This study reveals that the coupling analysis model is a very effective tool for simulating the hydraulic fracturing in concrete structures. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to draw attention to the lack, in current technical specifications, (i) of guidelines on the modelling of cast in situ reinforced concrete beam-column (RCBC) joints and, more specifically, (ii) for a given RCBC joint, of simplified procedures for evaluating if the fully rigid joint model is acceptable or not, having in view its effective stiffness. This is an important issue because, even though it is widely recognized that RCBC joints are a major source of deformation of cast in situ unbraced RC frames, there is no acknowledged simple procedure to assess the relevance of joint flexibility to the overall structural behaviour-as a consequence, the fully rigid joint model is commonly used without any reference to joint stiffness minimum required values. On the other hand, for steel frames, classification criteria for joints according to their stiffness have already been developed. This paper (i) shows that EN 1993-1-8: 2005 simplified classification criteria for steel joints according to their stiffness are inadequate for cast in situ RCBC joints, (ii) develops a modified version of these criteria, appropriate only for very particular conditions, which maintains their basic hypotheses but considers the specificities of RCBC joints and frames and (iii) in agreement with recently published results, concludes that, in some cases, RCBC joints should not be considered nominally rigid and thus their flexibility should be explicitly accounted for in the analysis of unbraced RC frames. The developed simplified classification criteria apply only to very particular cases-some guidance is therefore also provided on the development of general simplified classification criteria for RCBC joints. [ABSTRACT FROM AUTHOR]

School buildings have been classified by many of the design codes as important buildings, which have to withstand the earthquake excitations without any or with minor structural damages, and special care has to be given in their design and construction phases. This paper mainly aims to investigate the seismic performance of reinforced-concrete (RC) school buildings after 2011 Van earthquakes. The seismic performances of two damaged RC school buildings located in the earthquake-affected region are studied. First, the capacities of the selected buildings are assessed using nonlinear static procedures, and then, nonlinear dynamic time history analyses are performed to evaluate the seismic performances of the selected RC school buildings. Reasons for the observed damages are discussed. Further, recommendations are provided from the viewpoint of enhancing the structural capacity of the heavily damaged school building. As a result, to get an idea about the ductility demands imposed on the buildings, spectral acceleration values are compared with the seismic coefficients of the code that the buildings were adapted to. It can be concluded that the construction quality and detailing of the reinforcement are the key issues affecting the seismic performance of RC school buildings. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) monitoring was employed to detect and identify the extent of degradation resulting from reinforcing steel corrosion in concrete structures. Reinforced concrete samples were subjected to an accelerated corrosion test and corroded until they reached five different levels of mass loss of steel: 1, 2, 3, 4, and 5 %. The corrosion activity of all samples was continuously monitored using attached piezoelectric AE sensors and a multichannel data acquisition system. The results obtained from AE monitoring were analysed and compared to those obtained from half-cell potential (HCP) measurements, the amount of anodic current passing with time, and concrete cover cracking. The study analysed AE signal strength parameters including cumulative signal strength, historic index [ H( t)], and severity ( S) to detect the corrosion initiation, and subsequently, to classify the extent of damage following the corrosion progression. The study also aimed to correlate these parameters to both the degree of mass loss and concrete cover crack width. The results showed that the AE signal strength parameters can be exploited to characterize different degrees of damage from corrosion initiation and up to 5 % steel mass loss. These parameters can be analysed to detect the corrosion initiation earlier than the HCP test. This study also presented damage classification charts that can be used to correlate the level of steel mass loss and/or crack width to the AE signal strength parameters. Given these points, the outcomes of this investigation are substantial for advancing the application of acoustic emission for structural health monitoring in concrete structures. [ABSTRACT FROM AUTHOR]

Chloride is one of the main factors responsible for damages related to the corrosion of the concrete reinforcement in marine environments. It is known that this mechanism of degradation is directly related to environmental variables. Within this context, it can be inserted the global climate change. This paper deals with the effects of temperature and relative humidity changes on the service life of concrete structures affected by chloride attack. This way, three situations of environmental aggressiveness were simulated: past, current, and future. Then, models for predicting the chlorides penetration were analyzed to the three selected situations. So, a practical methodology is presented, and the results are consistent with the literature data. Among the results, it can be noted that changes in temperature and relative humidity identified in a period of 100 years were responsible for a reduction from 7.8 to 10.2 years of service life. Most standards provide a design service life of 50 years for reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Experimental evaluation of reinforced concrete beam specimens with different characteristics of reinforcement subjected to pushover and cyclic loading is presented. Plastic hinge rotation parameters are determined based on the idealization of pushover and hysteresis curves of reinforced concrete beam specimens constructed in two percentage of reinforcement (0.471% and 0.71%) with different ductile characteristics. The experimental test results provide a clear demarcation of the effect of types of loading and the types of reinforcement on the nonlinear performance characteristics of beam specimens. These results are helpful to update the nonlinear modeling parameters of beam components for the specific type of reinforcement used in the construction of a structure. The updated non-linear modeling parameters of beam components in lumped plasticity model are compared with the values of ASCE/SEI 41-06 (2007) used for the performance based design of structures. [ABSTRACT FROM AUTHOR]

The following study investigates the development and implementation of a crack width measurement system through the use of piezo-ceramic sensors as part of an active non-destructive health monitoring system for reinforced concrete important structures. As the world demand for economic and sustainable energy rises, the demand for important structures such as long-span bridges, nuclear power containment and offshore platform development has also dramatically increased. These multibillion dollar state-of-the-art structures require the most reliable and durable monitoring system to ensure their most economic yet prudent operation. The proposed system uses permanently embedded low-cost sensors to actively assess the health conditions of concrete beams throughout their lifetime span. In the current investigation, a series of concrete beam specimens have been tested in the lab to examine the adequacy and accuracy of low-cost piezo-ceramic sensors under a bulk wave system. The estimated crack widths from the results of the proposed system instrument measurements agree very well with the crack gauge records from the theoretical estimates and tested beams. The test results confirm the calibration and validity of the proposed system. The proposed system can provide the means of establishing an active structural health monitoring system that not only provides details on the extent of damage, but also its location within a reinforced concrete member. [ABSTRACT FROM AUTHOR]

The bond strength of concrete members at reversed cyclic loads is quite different from that of the concrete members at monotonic loads. Reversed cyclic loads produce a progressive bond deterioration that can lead to failure at cyclic stress levels lower than the ultimate stress at monotonic loads. In addition, the structural behavior of concrete members at dominant reversed loads reveals a dramatic reduction of energy dissipation in the hysteresis region due to a severe pinch effect. A method was proposed to predict the structural behavior of concrete members failing in bond after flexural yielding. The method takes into account the bond deterioration due to the degradation of concrete in the postyield range. To verify the bond behavior by the proposed method, predicted results were compared with the experimental data for concrete members at reversed cyclic loads, cited in the literature. Comparison of the experimental and calculated bond behavior of examined concrete members showed reasonable agreement. [ABSTRACT FROM AUTHOR]

The main purpose of this article is to study the behaviour of thin RC membranes under compression in one direction and tension in the perpendicular direction. The influence of the thickness on the behaviour of the concrete panel is investigated. To study the behaviour of the panels, an experimental programme was carried out. Six RC panels under pure shear were tested up to failure. As a result, new experimental stress-strain relationships of thin plates under pure shear are presented. Such relationships take into account the reduction of the compressive strength due to perpendicular tensile stresses and the influence of the thickness of the RC panels. The good experimental values obtained from this investigation validate the effectiveness of the low cost testing equipment developed for this study. This was a good achievement, because previous tests on this topic were performed using expensive equipment, which very few laboratories could afford. In general, the values obtained for the stress-strain relationships are approximately within the range proposed by other investigators. It is also shown that the strength capacity predicted by European codes is higher than that obtained from the experimental tests. The values predicted by ACI code are very conservative. [ABSTRACT FROM AUTHOR]

The main purpose of this article is to study compressed reinforced concrete membranes under perpendicular tensile stress. The state-of-the-art is presented and it shows that not much research has been done on this topic, probably because it needed very expensive laboratory equipment. In the current investigation, the authors have tried a new type of equipment, less expensive than that of previous investigations, and it proved to be adequate for the type of tests needed for studying this topic. The authors tested six reinforced concrete panels under pure shear up to failure. A parameter that was studied in these tests was the thickness of the membranes. This is of particular importance in webs or walls of beams under shear or torsion forces. From the experimental measurements, the authors have computed the principal directions and the values of the stresses and strains for the tested beams. In this article, these values are presented and the principal strains and stresses are compared with those at 45° and the two fairly agree with each other, particularly for the case of the stresses. [ABSTRACT FROM AUTHOR]

Seismic design of concrete structures is currently based on time-invariant capacity design criteria which do not account for environmental hazards. The significant progressive decay of strength and ductility of concrete structures exposed to damage, in particular due to reinforcing steel corrosion, shows that this approach should be revised to consider the deterioration over time of the seismic performance. This is important also for precast systems, for which most of structural members are often directly exposed to the atmosphere and environmental aggressiveness. This paper presents a probabilistic approach for the lifetime assessment of seismic performance of concrete structures considering the interaction of seismic and environmental hazards. The effectiveness of the proposed approach is shown by its application to multistory precast buildings exposed to corrosion. The results show that structures designed for the same seismic action could have different lifetime seismic performance depending on the environmental exposure. These results emphasize the importance of a life-cycle approach to both seismic assessment of existing buildings and seismic design of new structures, and indicate that capacity design criteria need to be properly revised to consider the severity of the environmental exposure. [ABSTRACT FROM AUTHOR]

A topology optimization procedure is presented as a tool for determining the distribution of external strengthening of concrete slabs, using Carbon Fiber Reinforced Polymer (CFRP). Although the procedure is applied to slabs in this work, the technique can be used in any concrete structure to be reinforced. Numerical simulations are performed using the Finite Element Method, in combination with the automated topology optimization procedure, to indicate the optimal region for placement of the reinforcement. The influence of some aspects of the slab's structural behavior on the optimization results is presented: concrete cracking, boundary conditions and reinforcement rate. A brief discussion is given of the similarity between the topology optimization results obtained by the maximum stiffness and ultimate strength criteria. Gains are found in the stiffness and strength of reinforced parts. A comparison with conventional reinforcement techniques demonstrates that topology optimization can be a useful tool for defining the region of reinforcement, allowing for material cost savings. [ABSTRACT FROM AUTHOR]

Past seismic events, including the 2009 L'Aquila earthquake and the 2012 Emilia earthquake, clearly demonstrated the inadequacy of the current design approach for the connection system of the cladding wall panels of precast buildings. To clarify this problem the present paper investigates the seismic behaviour of a traditional precast structural frame for industrial buildings with a new type of connection system of cladding panels. This system consists of a statically determined pendulum arrangement of panels, each supported with two hinges to the structure, one at the top and one at the bottom, so to have under seismic action a pure frame behaviour where the wall panels are masses without stiffness. Adding mutual connections between the panels, the wall cladding panels become part of the resisting structure, leading to a dual frame/wall system or to a wall system depending on the stiffness of the connections. The seismic behaviour of this structural assembly is investigated for different degrees of interaction between frame and panels, as well as for an enhanced solution with dissipative connections. The results of nonlinear static (pushover) analyses and nonlinear dynamic analyses under recorded and artificial earthquakes highlight the role of the wall panel connections on the seismic behaviour of the structural assembly and show the effectiveness of the dual frame/wall system with dissipative connections between panels. [ABSTRACT FROM AUTHOR]

Reinforcement corrosion is the major cause of damage and early failure of reinforced concrete structures worldwide with subsequent enormous costs for maintenance, restoration and replacement. Many methods used today for assessment of reinforcement corrosion are based on electrochemical techniques that determine the free corrosion potential or polarization resistance. Most of these methods always consider the B value in Stern-Geary equation as constant. However, B changes with different condition. In this paper, potentialdynamic method is used to characterize the corrosion of reinforcing steel. The corrosion rate of Q235 carbon steel is measured with concrete environment. B is calculated real-time. By this way, the error of reinforcement corrosion rate is minimized. [ABSTRACT FROM AUTHOR]

This paper describes one approach to the design of reinforced concrete (RC) bridge piers, using a three-hybrid multi-objective simulated annealing (SA) algorithm with a neighborhood move based on the mutation operator from the genetic algorithms (GAs), namely MOSAMO1, MOSAMO2 and MOSAMO3. The procedure is applied to three objective functions: the economic cost, the reinforcing steel congestion and the embedded CO emissions. Additional results for a random walk and a descent local search multi-objective algorithm are presented. The evaluation of solutions follows the Spanish Code for structural concrete. The methodology was applied to a typical bridge pier of 23.97 m in height. This example involved 110 design variables. Results indicate that algorithm MOSAMO2 outperforms other algorithms regarding the definition of Pareto fronts. Further, the proposed procedure will help structural engineers to enhance their bridge pier designs. [ABSTRACT FROM AUTHOR]

In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and mixture proportions, and depends on the curing conditions and the work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including shrinkage. Hence, the realistic prediction shrinkage strains of SCC are an important requirement of the design process for this type of concrete structures. This study reviews the accuracy of the conventional concrete (CC) shrinkage prediction models proposed by the international codes of practice, including CEB-FIP (1990), ACI 209R (1997), Eurocode 2 (2001), JSCE (2002), AASHTO (2004; 2007) and AS 3600 (2009). Also, SCC shrinkage prediction models proposed by Poppe and De Schutter (2005), Larson (2007), Cordoba (2007) and Khayat and Long (2010) are reviewed. Further, a new shrinkage prediction model based on the comprehensive analysis on both of the available models, i.e., the CC and the SCC is proposed. The predicted shrinkage strains are compared with the actual measured shrinkage strains in 165 mixtures of SCC and 21 mixtures of CC. [ABSTRACT FROM AUTHOR]

Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations (NDE) of concrete structures with surface bonded and embedded piezoelectric-ceramic (PZT) patches was studied. At first, the wave propagation mechanisms in concrete were analyzed. Then, an active sensing system with integrated actuators/sensors was constructed. One PZT patch was used as an actuator to generate high frequency waves, and the other PZT patches were used as sensors to detect the propagating wave. Scattered wave signals from the damage can be obtained by subtracting the baseline signal of the intact structure from the recorded signal of the damaged structure. In the experimental study, progressive cracked damage inflicted artificially on the plain concrete beam is assessed by using both lateral and thickness modes of the PZT patches. The results indicate that with the increasing number and severity of cracks, the magnitude of the sensor output decreases for the surface bonded PZT patches, and increases for the embedded PZT patches. [ABSTRACT FROM AUTHOR]

Vulnerable buildings and their rehabilitation are important problems for earthquake regions. In recent decades the goal of building rehabilitation and strengthening has gained research attention and numerous techniques have been developed to achieve this. However, most of these strengthening techniques disturb the occupants, who must vacate the building during renovation. In this study, a new strengthening alternative for RC structures, namely exterior shear walls, has been experimentally investigated under reversed cyclic loading. Using the proposed technique, it is possible to strengthen structures without disturbing their users or vacating the building during renovation. In this technique, shear walls are installed in parallel to the building's exterior sides. It has been observed that the usage of exterior shear walls considerably improve the capacity and sway stiffness of RC structures. The experimental results have also been compared and found to be in agreement with the numerical solutions. Post attached exterior shear walls behaved as a monolithic member of the structure. Design considerations for the exterior shear wall-strengthened buildings have also been discussed in the paper. [ABSTRACT FROM AUTHOR]

Monitoring the service condition of concrete structures requires the quantitative assessment of properties and corrosion rate of structural steels surrounded by concrete. A multi-cell sensor system that included a reference electrode, a chloride content sensor, a macrocell current unit and an electrical resistance measurement unit was developed. This system provided the following important electrochemical data in the cover-zone concrete on site: open circuit potential, macrocell current from anodes to cathode, chloride profile, concrete resistance and corrosion rate of built-in anodes. The experimental results show that the macrocell current increases when the chloride content in concrete is higher. Thus, monitoring the chloride content is a good method for monitoring the corrosion state. The chloride ion content and cover depth are the key factors that affect the electrical resistance of concrete. Without considering the temperature and time, a simplified model of the instantaneous corrosion rate of steel rebar in a concrete structure based on the measured chloride contents and concrete resistance was proposed. The test results further prove the reliability of this simplified predicting model. [ABSTRACT FROM AUTHOR]

Corrosion is an electrochemical process which requires electrolyte for the occurrence of corrosion reaction. Therefore it is necessary to calculate the effective corrosion rate with reference to the saturated area of concrete only when it comes to corrosion of steel reinforcement embedded in concrete. Theoretically and numerically the saturated area depends on the capillary zone porosity, gel zone porosity and their respective degree of saturation in the aggregate free volume of concrete which is a heterogeneous material in nature. This makes it important to deeply understand the effect of aggregate on corrosion in concrete. Investigation was carried out to find the effect of coarse aggregate volume on the corrosion rate and potential of reinforcement steel in concrete. The initiative for this research came from the observation that the interfacial transition zone around the steel bar in concrete is surrounded primarily by paste only and hence the coarse aggregate volume should not influence the corrosion rate principally. Also there are chances that some fine aggregate could be present in the vicinity of steel bar surface being finer than coarse aggregate which may affect the corrosion rate. The previous research data in this field was found to be limited and has a difference of opinion. Therefore, these factors have been investigated in this research. Prismatic concrete and mortar specimens were cast and their corrosion potential values were compared with each other to find the effect of the volume of coarse aggregate on corrosion. The experiment results showed that the effect of the volume of coarse aggregate on corrosion potential is not significant since the area around the steel bar especially in the case of deformed steel is mostly surrounded by paste only. The corrosion potential values obtained in the case of mortar and concrete specimens showed same averaged magnitude. This fact was further strengthened by measuring the corrosion mass loss and resulting corrosion rate in the two cases. Furthermore, in the light of experiment results obtained in this research, the numerical FEM model DuCOM developed by our research group at the University of Tokyo, Japan incorporating the effect of aggregate on corrosion rate and potential of corroding steel in concrete undertaken in the past has been successfully enhanced and verified in this research. [ABSTRACT FROM AUTHOR]

Abstract: This study proposes an algorithm of embedding cohesive elements in Abaqus and develops the computer code to model 3D complex crack propagation in quasi-brittle materials in a relatively easy and efficient manner. The cohesive elements with softening traction-separation relations and damage initiation and evolution laws are embedded between solid elements in regions of interest in the initial mesh to model potential cracks. The initial mesh can consist of tetrahedrons, wedges, bricks or a mixture of these elements. Neither remeshing nor objective crack propagation criteria are needed. Four examples of concrete specimens, including a wedge-splitting test, a notched beam under torsion, a pull-out test of an anchored cylinder and a notched beam under impact, were modelled and analysed. The simulated crack propagation processes and load-displacement curves agreed well with test results or other numerical simulations for all the examples using initial meshes with reasonable densities. Making use of Abaqus''s rich pre/postprocessing functionalities and powerful standard/explicit solvers, the developed method offers a practical tool for engineering analysts to model complex 3D fracture problems. [Copyright &y& Elsevier]

Corrosion of steel and rebar in concrete structures is one of the most frequent reasons for civil infrastructure failures. Thus, improving the effective corrosion sensor technology can greatly reduce cost and provide safe structures with long service lives. However, assessing the corrosion condition of rebars is not simple because they are buried in concrete. In this paper, using fiber Bragg grating (FBG), a corrosion sensor for monitoring steel rebars embedded in a concrete structure is developed and validated by experiments. Based on the fact that the volume and diameter of a rebar embedded in concrete will enlarge due to corrosion, an FBG packaged with fiber-reinforced plastics (FRP) is wrapped on the steel bar. During corrosion, the increase in the bar diameter leads to the increase in fiber strain, which can be measured by the shift of the wavelength of FBG. Performances of the corrosion sensor are validated by accelerating corrosion in lab experiments. The corrosion sensor is embedded in a concrete specimen put in a 5% sodium chloride solution with a constant current. Experimental results show that the corrosion sensor can monitor the concurrence of corrosion of rebars in concrete. The corrosion extent can be quantitatively evaluated through the change in the wavelength of FBG. Therefore, the corrosion sensor developed in this paper is feasible for monitoring the early corrosion of rebars in concrete. [ABSTRACT FROM AUTHOR]

Health monitoring of civil infrastructure systems has recently emerged as a powerful tool for condition assessment of structural performance. With the widespread use of modern telecommunication technologies, structures could be monitored periodically from a central station located several miles away from the field. Sensors are placed at several critical locations along the structure, and send structural information to the central station. This remote capability allows immediate damage detection, so that necessary actions that ensure public safety are taken. The goal of this research work is to evaluate the use of Fiber Optic sensing technology as a tool for structural health monitoring. To perform this task, a case study involving installation of Fiber Optic Sensors on a selected bridge structure during its construction phase was conducted. The bridge is located in the state of Florida, USA and is considered the first smart structure in this state. Static and Dynamic testing of the bridge were performed using loaded SU4 trucks. A 3-dimensional analytical finite element model of the bridge was developed and its results were compared to the test data. The study confirmed the accuracy of the sensors in estimating the bridge behavior under heavy truck loads. In addition, the sensors were connected to a data acquisition system permanently installed on-site. The acquisition system could be accessed through remote communication, which permits the evaluation of the bridge behavior under live traffic loads. Currently, live structural data under traffic loading is being transmitted continuously to the central maintenance office. The study revealed that the proposed health monitoring technology will enable practical, cost-effective, and reliable maintenance of bridge structures. [ABSTRACT FROM AUTHOR]

Ageing management and renewal of the operating license of existing NPP’s are at present the main problems of nuclear power industry. For the ageing management of concrete structures the OECD-Nuclear Energy Agency, Committee on the Safety on Nuclear Installations defined as the first priority ISI techniques for reinforced concrete structures having thick sections and areas not directly accessible for inspections. We discuss the NRI Rez research and development program in this field, as well as results, which will be used for qualification of the ISI techniques. [ABSTRACT FROM AUTHOR]